An axial flow gas turbine engine includes a compression section, a combustion section and a turbine section. The engine has a rotating rotor assembly. The rotor assembly includes a rotor disk-blade assembly which extends axially through the compression section, a rotor disk-blade assembly which extends axially through the turbine section, and a rotor shaft which extends axially connecting the rotor disk-blade assembly in the turbine section to the rotor disk-blade assembly in the compression section. A stationary stator assembly extends axially through the compression section and the turbine section of the engine. The stator assembly includes a case which circumscribes the rotor assemblies, supports which extend radially inwardly from the case for supporting the rotor assemblies, and stator vanes which extend radially inwardly from the case at a location upstream of each rotor assembly. The stator vanes prepare the gases for entry into an associated rotor disk-blade assembly.
A flow path for working medium gases extends axially through the sections of the engine. As the gases are flowed along the flow path, the gases are compressed in the compression section and burned with fuel in the pressurized combustion section to add energy to the gases. The gases flow to the turbine section where the rotor disk-blade assembly converts the energy in the gases into power to drive the compressor by turning the rotor shaft. The compressor and turbine sections have a special configuration, but only that of the combustion section is of interest here.
The combustion section includes a combustion chamber assembly extending circumferentially about an axis of symmetry. The combustion chamber assembly has an upstream end and a downstream end. The combustion chamber assembly includes an inner combustion chamber wall and an outer combustion chamber wall which extend between the ends. The walls are spaced radially leaving an annular combustion zone therebetween. The outer wall has holes disposed around its circumference at predetermined locations for admitting air for cooling and for the combustion process. A bulkhead assembly at the upstream end extends between the walls to join the walls together. The bulkhead assembly includes an inner ring, an outer ring and a bulkhead which extends radially between the two rings. The bulkhead is welded to the inner ring and outer ring to form an integral part.
The bulkhead has a first surface facing upstream and a second surface facing downstream. A dome-shaped hood for the combustion chamber extends over the upstream end of the combustion chamber assembly covering the first surface of the bulkhead. A plurality of lug mountings are an integral part of the hood and adapt the combustion chamber assembly for attachment in the engine. A plurality of openings are disposed circumferentially about the hood and the bulkhead. Each opening adapts the combustion chamber assembly to receive an associated fuel nozzle. Each fuel nozzle extends through the hood and the bulkhead for spraying fuel into the combustion chamber assembly.
A guide for each fuel nozzle is disposed in each opening in the bulkhead. The guides are spaced axially and spaced radially from the bulkhead leaving a passage for cooling air therebetween. A support, which is generally cylindrical in shape and extends upstream toward the combustion hood, is attached to the bulkhead and the guide to support the guide from the bulkhead. An anti-rotation element extends between each fuel nozzle and each support to restrain the fuel nozzle against rotation.
It is critical to the operative life of the engine that the angle of each fuel nozzle in relation to the lug mountings remains within predetermined limits. If the nozzle is positioned incorrectly, fuel may be sprayed onto the combustion chamber assembly walls, and the walls may be burned.
In order to repair the walls of the combustion chamber assembly individual wall elements are patched, replaced, or welded. Welding of minor cracks in the walls is standard procedure. Also, some of the dilution and combustion holes may need repairing. Patching or repairing these holes in the walls requires holes to be cut in the walls of the combustion chamber assembly. A type of holding apparatus, a vertical locating fixture, is used to measure the location for these local holes on the combustion chamber assembly and to hold the combustion chamber assembly while the holes are cut. The locating fixture uses the lug mountings of the combustion chamber assembly for support. The lug mountings are relatively strong in a direction parallel to the axis of the engine in comparison to the transverse direction, that is, the direction perpendicular to the axis of symmetry of the combustion chamber assembly.
The holes are cut utilizing a tool that has a chip formation action, such as, step drilling or end milling. The chip formation action exerts minimal transverse forces. Accordingly, the locating fixture exerts only enough force on the lug mountings to oppose the small transverse forces created by cutting local holes.
The locating fixture includes a base plate. An outer rim extends circumferentially about the plate and projects upwardly perpendicular to the plate. A plurality of pin holes extend radially through the outer rim of the plate. A plurality of locating pins extend through the pin holes, so that one locating pin extends through each pin hole. The locating pins adapt the fixture to engage the combustion chamber assembly by the lug mountings extending from the combustion chamber hood.
In addition to burning the walls, improper orientation of the fuel nozzles can cause further damage to the engine. The original engine has a temperature profile in the circumferential direction and the radial direction for the gases entering the high pressure turbine. The temperature profile of the gases exiting the combustion section around the annular combustion chamber assembly must substantially match a predetermined temperature profile for this to happen. Improper alignment of the fuel nozzles may cause the gases exiting the combustion section to have an altered temperature profile representing a temperature differential around the annulus, and/or the radius of the combustion chamber assembly. The gases exiting at a temperature profile substantially different than that of the original engine may excessively heat the rotor blades and the stator vanes in the turbine section causing the rotor blades and the stator vanes to oxidize and eventually fail. Typically, a repaired combustion chamber assembly may have a substantial temperature differential in its temperature profile. The temperature profile causes premature rotor blade and stator vane failure in the turbine section.
Accordingly, there is a inverse relationship between the quality of the repair and the rate of premature failure. Thus, the proper repair of the combustion chamber assembly each time it is repaired is vital to the durability the combustion chamber assembly and the turbine, and ultimately the performance of the aircraft.
The combustion chamber assembly is typically repaired two to three times in its life. Repairs may be performed on the supports for the fuel nozzle guides, the anti-rotation elements which rest on the supports, the openings for the fuel nozzle guides on the bulkhead and the walls of the combustion chamber assembly. Accessing the walls for repair operations, as described above, requires that the inner wall be removed. This provides access to components downstream of the bulkhead. Because the elements upstream of the bulkhead and areas on the upstream surface of the bulkhead needing repair are directly beneath the hood of the combustion chamber assembly, the industry practice is to remove the hood from the combustion chamber assembly to gain access to these damaged elements and areas.
Removing the hood is normally done by utilizing a cutting apparatus to make extensive cuts in the combustion chamber assembly. These cuts are wide because of the nature of the cutting wheel. A strong holding apparatus is used to resist the large forces developed during the cutting process. The first step is to mark an inside cut-line around the perimeter of the inner wall of the hood and to mark an outside cut-line around the perimeter of the outer wall of the hood. The next step is to place the combustion chamber assembly with the hood facing upwardly into the center of the cutting apparatus. Then the combustion chamber assembly is held firmly in place by a holding apparatus, such as a hydraulic sizing cluster.
The sizing cluster fits into the combustion chamber assembly and holds the combustion chamber assembly on its inner diameter at a position lower than the inside cut-line. The set-up of the sizing cluster is time consuming and difficult, because using the sizing cluster requires working with many small parts. Although the sizing cluster slows down the repair process, it has the ability to resist very large transverse forces exerted by the cutting wheel. Once the combustion chamber assembly is secure the cutting apparatus is used.
The cutting apparatus includes a crank arm, a fixed arm, an annular track and a cutting wheel. A gear system converts the rotary motion of turning the crank arm into the circumferential motion of the fixed arm traveling along the track. The cutting wheel is mounted on the end of the fixed arm. The cutting wheel is powered by an air system.
The cutting wheel is positioned along the inside cut-line and travels as many revolutions around the combustion chamber assembly as is necessary to separate the metal surfaces along the inside cut-line. The cutting wheel is then positioned along the outside cut-line and rotated until the metal surfaces separate. Because the cutting wheel uses an abrasive action to create the separations, the transverse forces created by it are far in excess of thoses created by the chip formation action used to repair the walls. Accordingly, the hydraulic sizing cluster is used because it exerts a large force to oppose the large transverse forces exerted by the cutting wheel even though it is time consuming to employ.
The above art notwithstanding, scientists and engineers working under the direction of applicants' assignee, are seeking to develop an apparatus for use in repairing combustion chamber assemblies which provides for an acceptable set-up time and which avoids massive cutting of the combustion chamber assembly to gain access to the bulkhead.